Transcript Main stages of Food Processing

Main stages of Food Processing
(Digestive System)
4 main stages of food processing: Ingestion, Digestion, Absorption, and
Elimination
Stage 1: Ingestion:
the act of eating
Stage 2: Digestion: the process of breaking down food into
molecules small enough for the body to absorb
Why? Because we cannot use macromolecules. We must break down the
polymers into smaller, usable components, and then rebuild them in our own
bodies
Polysaccharides simple sugars
Fatsglycerol and fatty acids
Proteinsamino acids
Nucleic acids nucleotides
Where does digestion start?
the mouth!
Chewing food increases the
surface area exposed to
digestive enzymes (salivary
amylase)
Stage 3: Absorption:
cells take up (absorb)
the small molecules
from the digestive
tract
Stage 4: Elimination:
undigested material passes
out of the digestive tract
Digestive System Organs
Overview
• Each organ has specialized food-processing functions
• After chewing and swallowing, it takes 5-10 seconds for food
to pass down esophagus into the stomach
• Food is broken down for 2-6 hours in stomach
• Final digestion and nutrient absorption in the small intestine
takes 5-6 hours
• In 12-24 hours, any undigested material passes through the
large intestine, and feces is expelled through the anus
Physical and chemical digestion begins in the mouth. Saliva contains salivary
amylase, an enzyme that hydrolyzes starch and glycogen into smaller
pieces.
• The tongue tastes food, and helps shape it into a ball called a bolus.
• The pharynx (throat) is a junction that opens to both esophagus and
trachea
• Peristalsis = waves of contractions from smooth muscles in the walls of the
digestive tract, pushes food along
Stomach has a very elastic wall so it can stretch if
you eat a lot of food. It secretes very acidic gastric
juice (digestive fluid, pH2). Also pepsin, enzyme that
hydrolyzes proteins
Stomach
Stomach has a coating of
mucus, secreted by
epithelial cells, to protect
it from acidic gastric juice
• It doesn’t completely
protect it so the
epithelium is continually
damaged and completely
replaced by mitosis every
3 days
• Pyloric sphincter-at end
of stomach before small
intestine
Duodenum
• the first 25 cm or so of the small
intestine, most digestion occurs here
• Where food molecules from stomach
(acid chyme) mixes with digestive
juices from the pancreas, liver, gall
bladder, and gland cells of the
intestinal wall
• Liver has many functions, including
production of bile
• Gall bladder stores the bile until
needed
• Pancreas enzymes include proteases
(protein-digesting enzymes)
Small intestine: duodenum, jejunum, ileum
• Most absorption takes place in the
small intestine
• Has a huge surface area (300 m2) –
roughly the size of a tennis court
• Folds and tiny projections called villi
and microvilli increase surface area for
absorption
Large intestine (colon)
• Main function: reclaiming water
• 90% of water in digestive tract is
reabsorbed in small intestine and
large intestine
• Feces (waste) becomes more solid
as it moves down the large
intestine.
– Diarrhea? Not enough water was
reabsorbed (usually because lining of
colon is irritated by a bacterial
infection)
– Constipation? Feces moved too
slowly and too much water was
reabsorbed
Rectum and anus
• Got gas? As a byproduct of their
metabolism, many colon bacteria
generate gases, including methane
and hydrogen sulfide
• Feces are stored in the rectum until
they can be eliminated through the
anus